On Mon, 6 Dec 2021 11:11:51 +0000, Christophe Leroy wrote:

Unmapping a fixmap entry is done by calling __set_fixmap()
with FIXMAP_PAGE_CLEAR as flags.

Today, powerpc __set_fixmap() calls map_kernel_page().

map_kernel_page() is not happy when called a second time
for the same page.

[...]

Applied to powerpc/fixes.

[1/1] powerpc/fixmap: Fix VM debug warning on unmap
      https://git.kernel.org/powerpc/c/aec982603aa8cc0a21143681feb5f60ecc69d718

cheers